The distribution of oxygen at the Ni81Fe19/Ta interface

The knowledge of how oxygen atoms are distributed at a magnetic-metal / oxide, or magnetic-metal / non-magnetic-metal interface, can be an useful tool to optimize device production. Multilayered Ni81Fe19 / Ta samples consisting of 15 bilayers of 2.5 nm each, grown onto glass substrates by magnetron sputtering from Ni81Fe19 and Ta targets, have been investigated. X-ray absorption near edge structure, extended X-Ray absorption fine structure, small angle X-ray diffraction, and simulations, were used to characterize the samples. Oxygen atoms incorporated onto Ni81Fe19 films during O2 exposition are mainly bonded to Fe atoms. This partial oxidation of the Ni81Fe19 surface works as a barrier to arriving Ta atoms, preventing intermixing at the Ni81Fe19 / Ta interface. The reduction of the Ni81Fe19 surface by the formation of TaO x is observed.Comment: 14 pages, 9 figures, accepted for publication in Advances in Materials Science and Engineerin

Non-commutative geometry and the standard model vacuum

The space of Dirac operators for the Connes-Chamseddine spectral action for the standard model of particle physics coupled to gravity is studied. The model is extended by including right-handed neutrino states, and the S0-reality axiom is not assumed. The possibility of allowing more general fluctuations than the inner fluctuations of the vacuum is proposed. The maximal case of all possible fluctuations is studied by considering the equations of motion for the vacuum. Whilst there are interesting non-trivial vacua with Majorana-like mass terms for the leptons, the conclusion is that the equations are too restrictive to allow solutions with the standard model mass matrix.Comment: 21 pages. v2: some comments improve

Spin Polarization and Magneto-Coulomb Oscillations in Ferromagnetic Single Electron Devices

The magneto-Coulomb oscillation, the single electron repopulation induced by external magnetic field, observed in a ferromagnetic single electron transistor is further examined in various ferromagnetic single electron devices. In case of double- and triple-junction devices made of Ni and Co electrodes, the single electron repopulation always occurs from Ni to Co electrodes with increasing a magnetic field, irrespective of the configurations of the electrodes. The period of the magneto-Coulomb oscillation is proportional to the single electron charging energy. All these features are consistently explained by the mechanism that the Zeeman effect induces changes of the Fermi energy of the ferromagnetic metal having a non-zero spin polarizations. Experimentally determined spin polarizations are negative for both Ni and Co and the magnitude is larger for Ni than Co as expected from band calculations.Comment: 4 pages, 3 figures, uses jpsj.sty, submitted to J. Phys. Soc. Jp

Transición eléctrica en multicapas delgadas de VO2/SiO2 y VO2/TiO2, sintetizadas en substratos de Si(100)

Multicapas de VO2/SiO2 y VO2/TiO2 de tres periodos fueron sintetizadas sobre substratos monocristalinos de Si (100) con buffer de SiO2 y TiO2, respectivamente. La caracterización estructural por difracción de rayos X (XRD) de ambas multicapas, a temperatura ambiente, mostraron el pico de difracción correspondiente al plano cristalográfico (011) bien definido evidenciando la presencia de la fase VO2 (M1). Para [VO2/TiO2] x 3, el pico de difracción originado por los planos (011), mostró un ligero corrimiento hacia valores más bajos del ángulo, en relación al pico patrón. Las medidas del transporte electrónico en función de la temperatura, para las multicapas [VO2/SiO2] x 3, mostraron transición eléctrica a temperaturas de 55 °C y 58 °C y ancho de histéresis (H), de 9 °C y 6 °C, respectivamente. En el sistema [VO2/TiO2] x 3, la transición eléctrica ocurrió a 74 °C, con un ancho de histéresis sumamente estrecho (2 °C). Nuestros resultados sugieren que el comportamiento de la histéresis, así como el corrimiento mostrado por el pico experimental del plano (011), puede ser interpretado como consecuencia de la difusión de iones de Ti+4 hacia los sitios del V+4 en el VO2, debido a la alta temperatura del sustrato durante la deposición. Así, las impurezas de Ti+4 difundidas, actúan como núcleos de transformación de fase en el VO2, disminuyendo la energía de activación de la transformación de fase, explicando de esta manera la estreches de la histéresis observad

Missouri 2011 Corn Performance Tests

This report is published by the MU Variety Testing Program, Division of Plant Sciences, University of Missouri. The work was supported by fees provided by companies submitting hybrids for evaluation. The University of Missouri's hybrid performance testing program began in the mid-1930s, with results first published in 1937. The number of entries in the program has grown from fewer than 50 in the early years to more than 250 today. The large number of commercial hybrids available makes selection of a superior hybrid difficult. To select intelligently, producers need a reliable, unbiased, up-to-date source of information that will permit valid comparisons among available hybrids. The objective of the MU Variety Testing Program is to provide this information

Spin-accumulation in small ferromagnetic double barrier junctions

The non-equilibrium spin accumulation in ferromagnetic double barrier junctions is shown to govern the transport in small structures. Transport properties of such systems are described by a generalization of the theory of the Coulomb blockade. The spin accumulation enhances the magnetoresistance. The transient non-linear transport properties are predicted to provide a unique experimental evidence of the spin-accumulation in the form of a reversed current on time scales of the order of the spin-flip relaxation time.Comment: 4 pages, 3 figures, to appear in PR

Large Magnetoresistance Ratio in Ferromagnetic Single-Electron Transistors in the Strong Tunneling Regime

We study transport through a ferromagnetic single-electron transistor. The resistance is represented as a path integral, so that systems where the tunnel resistances are smaller than the quantum resistance can be investigated. Beyond the low order sequential tunneling and co-tunneling regimes, a large magnetoresistance ratio at sufficiently low temperatures is found. In the opposite limit, when the thermal energy is larger than the charging energy, the magnetoresistance ratio is only slightly enhanced.Comment: updated versio

Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $\delta$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $\delta$ can become negative.Comment: 11 pages, 2 eps figure

Mesoscopic Tunneling Magnetoresistance

We study spin-dependent transport through ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic Coulomb blockade regime. A general transport equation allows us to calculate the conductance in the absence or presence of spin-orbit interaction and for arbitrary orientation of the lead magnetizations. The tunneling magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is calculated and its probability distribution presented. We show that mesoscopic fluctuations can lead to the optimal value of the TMR.Comment: 5 pages, 3 eps figures included using epsf.sty. Revised text and improved notation, fig. 2 removed, explicit equations for the GSE case adde

Spin flip scattering in magnetic junctions

Processes which flip the spin of an electron tunneling in a junction made up of magnetic electrodes are studied. It is found that: i) Magnetic impurities give a contribution which increases the resistance and lowers the magnetoresistance, which saturates at low temperatures. The conductance increases at high fields. ii) Magnon assisted tunneling reduces the magnetoresistance as $T^{3/2}$, and leads to a non ohmic contribution to the resistance which goes as $V^{3/2}$, iii) Surface antiferromagnetic magnons, which may appear if the interface has different magnetic properties from the bulk, gives rise to $T^2$ and $V^2$ contributions to the magnetoresistance and resistance, respectively, and, iv) Coulomb blockade effects may enhance the magnetoresistance, when transport is dominated by cotunneling processes.Comment: 5 page